Usually, touch panels are input devices which are respectively attached onto display devices such as LCDs (Liquid Crystal Displays), PDPs (Plasma Display Panels), OLED (Organic Light Emitting Diode) displays, and AMOLED (Active Matrix Organic Light Emitting Diode) displays or which are respectively built in the display devices, to thus generate an input signal corresponding to a position where a touch input occurs using a touch unit such as a finger or a touch pen.
The touch panels are chiefly mounted respectively on mobile devices such as mobile phones, PDAs (Personal Digital Assistants) or PMPs (Portable Multimedia Players). Besides, touch input devices are being used over all industries such as navigation terminals, netbook computers, notebook computers, DIDs (Digital Information Devices), desktop computers that use touch input supporting operating systems, IPTVs (Internet Protocol TVs), the most advanced fighter aircrafts, tanks, and armored vehicles.
Various types of conventional touch panels are disclosed, but resistive-type touch input devices having simple manufacturing processes and inexpensive manufacturing costs have been used most widely. The resistive-type touch panels, however, have low transmittance and undergo the pressure applied to respective substrates, to thereby cause problems that inevitable loss of durability occurs over lapse of use time, malfunction or misrecognition frequently takes place due to changes in resistance values depending upon the external environment, and uniformity of surface resistance is strictly needed to thus cause a very poor yield. It is also difficult to apply the resistive-type touch panels for a large screen display, and it is fundamentally difficult to recognize multiple touches.
Capacitive-type or electrostatic capacitive-type touch panels that were developed as an alternative to the resistive-type touch panels detect touch inputs in a non-contact mode and have a solution to various problems of the resistive-type touch panels.
FIG. 1 shows the structure of a conventional electrostatic capacitive-type touch panel. Referring to FIG. 1, the conventional capacitive-type touch panel includes transparent conductive films that are formed on the top and bottom surfaces of a transparent substrate 10 made of film, plastic or glass. Metal terminals 12 for applying voltage are formed at each of four corners of the transparent substrate 10. The transparent conductive film is formed of transparent metal such as ITO (Indium Tin Oxide) or ATO (Antimony Tin Oxide). The metal terminals 12 respectively formed at the four corners of the transparent conductive film are formed by printing low resistivity conductive metal such as silver (Ag). A resistor network is formed around the metal terminals 12. The resistor network is formed in a linearization pattern in order to transmit a control signal equally on the entire surface of the transparent conductive film. A protective film is coated on top of the transparent conductive film including the metal terminals 12.
The capacitive-type touch panels operate as follows. A high-frequency alternating-current (AC) voltage applied to the metal terminals 12, is spread to the whole surface of the transparent substrate 10. Here, if a finger 16 (or a conductive material touch unit) lightly touches the top surface of a transparent conductive film of the transparent substrate 10, a certain amount of electric current is absorbed into the human body and changes in the electric current are detected by a built-in electric current sensor of a controller 14, to thus calculate the amount of electric current at the four metal terminals 12, respectively, and to thereby recognize a touch point.
The capacitive-type touch panel employs a soft touch mode to thus have a long life, uses only a sheet of the transparent substrate 10, to thus have a high light transmittance, and makes a special metal coating treatment on a contact surface thereof, to thus have an advantage of robustness. In particular, the capacitive-type touch panel has a narrow width of a non-active area which makes it impossible to detect touch inputs at the panel edge portions, to thus have an advantage of enabling a mechanical instrument to be made in a slim form at the time of being coupled with a display device.
However, the electrostatic capacitive-type touch panel needs an expensive detector in order to detect a magnitude of minute electric current, and further needs an analog-to-digital (ADC) converter for converting detected analog electric current to digital electric current, to accordingly cause an inevitable price increase. In addition, there may raise a problem that a response time is prolonged due to the time consumed for converting analog signals to digital signals. Above all, since a difference in magnitude between an electric current detected when a touch input occurs and a usual electric current measured before the touch input is very small, there may cause had detection sensitivity and high noise sensitivity. For example, assuming that a magnitude of electric current that is leaked from one of the metal terminals 12 when no touch input occurs is 1 μA and a magnitude of electric current that is leaked from the same one metal terminal 12 when a touch input occurs is 2 μA, detection of the difference between the minute electric currents by using a circuitry means may cause degradation of accuracy and signal recognition errors due to noise.